This invention involves an apparatus which attaches to a spindle assembly and controls the depth of penetration of a drill or router relative to the pressure foot. Because the pressure foot rests on the cutting surface, the depth of penetration by a drill or router into the cutting surface is also controlled. The present invention stops the penetration without stopping the vertical, known as the Z-axis, drive by providing a means for compression of the spindle assembly that internally absorbs the excess travel along the Z-axis.
One typical configuration for a spindle assembly includes a top-mounted cylinder and piston that raises and lowers the spindle assembly. The common names for these are the "select cylinder" and "select cylinder piston". The cylinder may be filled with air or hydraulic fluid. Air or hydraulic pressure is applied to the lower side of the piston to lift the spindle assembly from the cutting surface. Likewise, pressure is applied to the upper side of the piston when the spindle assembly is placed into operating position against the cutting surface. Usually, air pressure during operation of the spindle is maintained between 50 psi and 80 psi.
Once the cutting process begins, the drill or router on the spindle is driven into the cutting surface by externally applied force along the vertical or Z-axis. Control of the depth of penetration into the cutting surface is important for precision work, such as making circuit boards. Except in very expensive spindle assemblies, the depth is controlled only by setting the distance of travel for the Z-drive.
The present invention addresses the problem of maintaining a constant depth of penetration by adding three features to the typical spindle assembly. First, a scalar measuring device, such as a micrometer, is attached to the spindle to provide a reference measurement between the spindle and the pressure foot. This measurement thereby sets the limit or depth to which the drill or router may penetrate. Second, a mechanical stop is attached to the pressure foot linkage, so as to prevent the spindle from penetrating beyond the preset depth. Third, a pressure regulator is attached to the air (or hydraulic) system for the select cylinder to reduce the pressure inside the select cylinder and thereby allow compression by the select cylinder piston. In lieu of this pressure regulator, a compression cylinder or spring can be attached anywhere between the spindle and the Z-drive to provide for the needed means to absorb excessive downward travel. Working together, these improvements allow the Z-drive to operate normally while maintaining a constant depth of penetration relative to the cutting surface, as referenced to the pressure foot.
Some spindle assemblies are configured without a select cylinder and piston, so that the Z-drive is attached directly to the top of the spindle. In such cases, a compression cylinder and piston can be mounted anywhere between the spindle and the Z-drive. It should also be noted that an alternate means for compression, such as a spring, can be utilized to accomplish the same purpose.
In spindle assemblies that feature a locking device that secures the spindle and pressure foot together, the locking device must be disabled. One way of doing this is to install a switch. This switch can be further linked to the mechanical stop so that the locking device is automatically disabled when the mechanical stop is in position for use.
Likewise, to automate the reduction of pressure in the select cylinder, a switch can be linked to the mechanical stop to engage the pressure regulator when the mechanical stop is in position for use.
The primary advantage of the present invention is the increased precision for depth tolerances that is gained by modifying existing types of spindle assemblies. Another advantage is that the present invention can be installed in machines already in service without limiting their performance capabilities. Also, the present invention can be added to new spindle assemblies during the manufacturing process. Another advantage is that the improved depth control generates less scrap material during drilling and routing processes. Cutting tool life can be extended by elimination of excessive drilling and routing. Still another advantage is the increased ease of setting the desired depth of penetration into a cutting surface. When the cutting task is repetitive, setup time is reduced because the depth measurement does not have to be reset for each cutting surface. More advantages will be obvious from a further review of the drawings and specifications contained herein.
The present invention differs from depth controls previously disclosed in U.S. Pat. No. 4,530,625 (which provides for a hydraulic stop and override system), U.S. Pat. No. 4,436,460 (which compensates for depth by a sensor activated motor drive), and U.S. Pat. No. 5,123,789 (which places controls on the Z-drive).